Adsorption isotherms-microscopic modelling: Part II

Abstract

A lattice formalism using "spin variables" is employed to analyse multi-state models for the adsorption of neutral dipoles. In particular, a spin-1/2 (two-state) model incorporating permanent and induced dipole moments of the solvent and the organic adsorbate, substrate interactions, and discreteness of charge effects is analysed. The resulting Generalized Ising Hamiltonian is solved under mean field approximation (MFA) in order to derive the adsorption isotherm for organic molecules. A few spin-1 (three-state) models are also analysed under MFA to describe the competitive adsorption of multi-state solvent and organic dipoles, and the appropriate equilibrium relations are derived. The unification and isomorphosm existing at the Hamiltonian level for several diverse realizations, such as adsorption of ions and solvent/organic molecules, is indicated. The possibility of analysing phase transitions using this generalized approach is briefly indicated.